As the Mars roverCuriosity, a $2.5 billion robot the size of a Mini Cooper, touched down last night, one billionaire was already planning the next logical step -- sending humans there.

"I'm confident at this point that it can be done," Elon Musk told "Nightline" in an interview at SpaceX headquarters in Los Angeles. "I think we'll be able to send, probably, the first people to Mars in roughly 12 to 15 years. That's my estimate."

Musk, who made his billions as an Internet entrepreneur, wants to bring Silicon Valley ingenuity to a space exploration process that, until recently, has been something only governments tried to tackle.

He entered the space race in 2010 with his company's Falcon 9 rocket and Dragon capsule, reusable spacecraft built with the goal of taking astronauts into space and returning them safely to Earth.

Musk said he is aware he has competitors in this new space race -- one reason why SpaceX does not patent any of the top-secret technology it creates.

"The rockets we're building right now could certainly send probes to Mars, like the Mars rovers and that kind of thing," he said. "But the rockets we hope to build in the future are the ones that could take people and cargo to Mars and establish a Martian base."

And he has big plans for Mars -- not just taking people there, but making it possible for people to thrive there and even establish businesses.

"Mars is the only place in the solar system where it's possible for life to become multi-planetarian," Musk said. "We could make Mars like Earth…it's more than our life raft, it's like backing up the biosphere."

One of the biggest challenges of colonizing the red planet is making the trip affordable for the average American, he said, which is "extremely difficult."

"We know it's possible to get there," Musk said. "You would be moving to Mars, so a round trip ticket, it has to be no more than half a million dollars, so roughly, a middle-class house in California, and at this point, I would say, I know it's possible."

He said the key to conquering the cost barrier is designing a reusable rocket.

"If you look at something like a Boeing 747 -- that's over a quarter of a billion dollars, buying a 747," he said. "You need two of them for a round trip. But nobody is paying half a billion dollars to fly from L.A. to London. It's a few thousand dollars, and that's because you reuse that aircraft multiple times, you use it thousands of times."

"The acquisition costs -- the cost of building that aircraft in the first place -- is only a small portion of your ticket price," he said. "If we could then have a reusable rocket, then the cost of the flight would be a lot closer to the cost of fuel."